Method of making an explosive booster



May 25, 1965 M. A. COOK ETAL METHOD OF MAKING AN EXPLOSIVE BOOSTER Original Filed July 13, 1959 INVENTORS MELVIN A. (00K DOUGLAS H PACK United States Patent 3,185,017 METHOD OF MAKING AN EXPLOSIVE EUOSTER Melvin A. Cook and Douglas H. Pack, Salt Lake @ity,

Utah, assigrrors to lutcrnlountain Research and Engineering Company, Inc., Salt Lake (Iity, Utah, :1 corporalieu of Utah Original application July 13, 1959, Ser. No. 826,539. new Patent No. 3,037,453, dated June 5, 1962. liividetl and this application Oct. 24, 196i Ser. No. 7%,884

2 Claims. (Cl. 36-1) This invention relates to detonating means for cxplosives and more particularly to boosters for relatively insensitive explosive compositions. This application is a division of our copending application Serial No. 826,539, filed July 13, 1959, now U.S. Patent No. 3,037,453.

insensitive explosives, containing a high percentage of ammonium nitrate and containing non-explosive organic sensitizers, have found wide application as blasting cxplosives. Prilled ammonium nitrate containing 94 percent ammonium nitrate and 6 percent fuel oil and aqueous slurries of coarse TNT-ammonium nitrate are examples of such insensitive explosives. Such compositions are not detonatable by blasting caps and prior art methods for detonating them include the use of dynamite or relatively large quantities of fine-grained TNT primers, for example, which are detonated by blasting caps or Primacord. These methods suffer from the disadvantage of being expensive and further, dynamites, fine TNT and blasting caps are very sensitive to heat and shock.

In modern large diameter blasting operations using high ammonium nitrate explosives, Primacord fuse is the most desirable detonator. The high ammonium nitrate explosives are not dependably detonatable by Primacord, however, and require a booster. Unfortunately, only a few of the most sensitive explosives are consistently capable of detonation by Primacord containing the minimum content of PETN, e.g., about 50 grains of PETN per foot of Primacord. Of those boosters that are operable, relatively large quantities of expensive boostering compositions are required consistently to booster the ammonium nitrate explosive.

Accordingly, it is an object of the present invention to provide a booster for insensitive explosives which is consistently detonatable by minimum PETN content Primacord.

It is another object of the invention to provide such a booster which consistently detonates high ammonium nitrate explosives in either the Wet or dry state.

A further object of the invention is to provide such a booster which is inexpensive and utilizes a minimum of the expensive Primacord-sensitive materials.

Among the other objects of the invention, one is to provide a protected core booster in which Primacord is readily and simply threaded for use in blasting operations.

Another object of the invention is to provide a booster which is much less sensitive to heat, shock, impact, friction and other influences causing accidental initiation than prior art boosters.

Another object is to provide improved methods for making boosters.

Other objects and advantages will be apparent to those skilled in the art.

We have now found that the most important factor in a booster with respect to its boostering activity on insensitive explosives is its detonation pressure or brisance. The term brisance" connotes shattering action which is dependent on the detonation pressure. in the hydrodynamic theory of detonation, the detonation pressure is proportional to the density of the explosive and the square of the detonation velocity.

Examples of explosives of high brisance are cast or 3,135,017 Patented May 25, 1965 pressed pentolite (PETN-TNT), TNT, tetryl, tetrytol (tctryl-TNT), cyclotol (RDX-TNT), composition B (RDXTNT-wax) and Ednatol {EDNA-TNT). The more inexpensive of these explosives are not detonatable by Primacord, however.

It has been found that PETN, PETN-TNT mixtures, RDX and cyclotol are detonated by Primacord, but their high cost and the relatively large quantities required make it uncconomical to use them as boosters.

The improved booster of the invention generally comprises a core of Primacord-sensitive explosive material surrounded by a compacted sheath of Primacord-insensitivc explosive material of high brisance, said booster having at least one perforation extending through said sheath and said core adapted to receive a detonating fuse, said core comprising a tube containing Primacord-sensitive explosive adjacent to and defining at least a portion of the perimeter of said perforation.

One embodiment of the invention is such a booster wherein said Primncord-sensitive explosive is pentaerythritol tetranitrate contained within said tube and wherein said Primacord-insensitive explosive is cast TNT. A further embodiment is such a booster wherein said Primacordsensitive explosive is pentaerythritol tetranitrate contained within said tube and said Primacord-insensitive explosive is a cast mixture of 25 percent by weight of TNT and percent by weight of composition 13.

A preferred form comprises such a booster wherein two perforations are provided and wherein the core comprises a tube in a figure ti configuration containing Primacordsensitive explosive adjacent the perimeter-s of said perforations. An alternative embodiment is such a booster wherein the tube containing Primacord-sensitive explosive is wound in helical fashion adjacent to and defining the perimeter of said perforation.

The method of the invention generally comprises supporting a rod, placing a tube containing Primacord-sensitive explosive contiguous to said rod, compacting a sheath of Primacord-insensitive explosive about said rod and tube, and removing said rod from said compacted sheath to provide a perforation through the sheath adapted to receive a detonating fuse. A preferred method involves casting the sheath about the rod and tube. The tube of Primacord-sensitive material may be helically wrapped about the rod, or if two rods are provided, the tube may be wound in figure 8 fashion about said rods.

FIGURE 1 is a view of the tube of Primacord-sensitive explosive positioned on a pair of rods prior to compacting the sheath of Primacord-insensitive explosive about it.

FIGURE 2 illustrates the casting of Primacord-insensitive explosive about the tube according to the invention.

FIGURE 3 is a view of a finished booster made in accordance with the invention.

FIGURE 4 is a cross-sectional view of the booster of FIGURE 3.

The booster as shown in FIGURES 3 and 4 comprises a compact sheath ll of l rimacord-Insensitive explosive. Within the sheath 19 is a tube 11 containing Primacordsensitive explosive 12 adjacent to the perforation 13. In the embodiment shown. two holes 13 extend through the booster for receiving Primacord detonating fuse and the tube 11 is disposed in FIGURE 8 configuration with respect to the holes 11.

While the assembly may assume any desired shape, it is preferred to use the cylindrical form shown for economy of material and ease of manufacture. It is preferred to employ two holes 13 to loop the Primacord fuse through, although the boosters of the invention are dependably detonated by Primacord passing through only one hole. Accordingly, the boos er may have only one hole with the tube ll disposed in helical fashion about the periphery of the hole. In a further modification, two

d holes may be used and the tube helically disposed about each hole.

As shown in FIGURES 1 and 2, a base 14 is provided with a pair of upstanding pins or rods 15. The tube 11 is wound about the rods 15, the winding being in figure 8 form, although helical winding of the tube about the rods may also be used. A form 16 of metal or cardboard is placed over the wound rods and rnolten Primacord-insensitive explosive 17 is poured into the form from spout 16. After the assembly has hardened, it is removed from the base 14 to yield a booster as shown in FIGURE 3 having two perforations extending therethrough.

Porms 16 made of cardboard or paper are satisfactory and it has been found unnecessary to remove the form from the booster in such cases.

An alternative method of compacting the explosive about the core comprises pressing particulate explosive in the form to yield a compact shaped booster.

The tube 11 may be made of plastic such as polyethylene, vinyl chloride, vinylidene chloride, polyethylene terephthalate or any of the synthetic rubbers or it may be of cellulosic material such as regenerated ceilulose, cellu lose acetate or cellulose nitrate. Additionally, Primacord itsef, which contains fine grained PETN, may be used as the tube containing Primacord-sensitive explosive.

The Primacord-sensitive explosive 12 contained within the tube is preferably fine-grained material and may be PETN, RDX, amatol, tetryl and fine-grained TNT. The latter is lrimacord-sensitive whereas coarse or cast TNT is Primacord-insensitive. If fine-grained TNT is used in the tube and the sheath is cast TNT, a sufficiently heavy walled tube must be used to insulate the TNT within the tube from the heat of the molten TNT which is cast to form the sheath.

The Primacord-insensilive explosive forming the sheath It] may be cast or pressed TNT, composition B (59% RDX40% TNT-1% wax) or composition B-TNT mixtures. The above possess high brisance but are not consistently detonatable by Primacord containing 50 grains of PETN per foot.

It has been found that cylindrical boosters about three inches in diameter and two inches long provided with two holes made in accordance with the invention consistently detonate the insensitive ammonium nitrate explosives. Such boosters contain about 300-400 grams of Primacord-insensitive explosive. The tube 11 containing the Primacord-sensitive explosive 12 may contain about to grams of PETN or its equivalent. For the least sensitive explosives in the sheath 10, more Primacord-sensitive explosive should be used to achieve high order detonations. For example, forty boosters were prepared in accordance with the invention, utilizing one foot lengths of 0.263 inch internal diameter 0.020 inch thick (wall thickness plastic tubes containing about 10 grams of PETN each). Twenty of such tubes were wound about the rods 15 in figure 8 fashion as shown in FIGURE 1 and twenty were wound helically on the rods 15. Ten of each of the groups were then formed into boosters by casting a cylinder 3 inches in diameter by 2 inches high from 100% TNT. Ten of each of the boosters were formed in the same manner by casting TNT, 75% composition B. The boosters were then fired with 50 grain PETN/foot Primacord threaded through one only of the holes. All forty of such boosters fired, giving a detonation percentage of 100%.

As indicated above, Primacord itself may be used as the tube containing the Primacord-sensitive explosive. In a series of tests, we have found that boosters made from 6 inch to one foot lengths of 50 grain PETN/foot Primacord wound in figure 8 fashion contained within a sheath of 350 grams of cast 75% composition B, 25% TNT according to the invention yield 100% detonations with a 50 grain PETN/foot Primacord strand running through one hole only. Such boosters cut a clean hole through a one inch thick, 6 x 6 inch steelplate.

Similarly, we have found that one foot lengths of 200 grain PETN/foot and 400 grain PETN/foot Primacord wound in a figure 8 core yield detonations when cast 100% TNT is used as the sheath. As a control, cast cylinders of 100% composition B without a core failed to yield 100% detonation with 50 grain PETN/foot Prima- CQI'ti threaded through both holes.

While it is not intended to be bound by any theory of operation, it is believed that the tube 11 of Primaco'rdsensitive explosives, adjacent and peripheral to the perforations, yield detonation waves that interact and reinforce each other to produce a high intensity shock effect. thereby detonating the main booster charge 10 which is otherwise not detonatablc by Primacord.

In use, a Frimacord fuse, such as 50 grain PETN/foot, is threaded through one or more of the holes 13 and knotted to prevent the removal of the booster from the fuse. The booster may be inserted in a priming cartridge of ammonium nitrate explosive or preferably lowered by itself into the bore hole by suspending it on the Primacord line at the appropriate position in the hole. The main charge is then introduced simply by pouring the loose or slurry explosive into the hole. The Primacord use is initiated electrically as is well known in the art.

Either cost or pressed boosters may be prepared in accordance with the invention. Cast boosters are preferred because they do not crumble upon wetting or subjected to rough handling. Cast boosters are also less water-sensitive.

We have thus described novel boosters which are consistently operative for boostering ammonium nitrate explosives which employ a minimum of expensive materials and whch are consistently detonatable by 50 grain Primaeord. White the invention has been described in terms of certain embodiments, these are to be considered illustrative rather than limiting and it is intended to cover all further embodiments that fall within the spirit and scope of the appended claims.

\Ve claim:

1. The method of making a booster for insensitive explosives comprising supporting a rod on a base in upstanding relation thereto, wrapping a flexible tube containing Priinacord-sensitive explosive around said rod, compacting a sheath of Primacord-insensitive explosive on said base about said rod and tube and removing said rod and base from said compacted sheath to provide a perforation through the sheath adapted to receive a detonating fuse.

2. The method of making a booster for insensitive explosives comprising supporting a pair of rods on a base normal thereto and parallel to each other, winding a flexible tube containing Primacord-sensitive explosive around said rods in figure S configuration, casting a sheath of Primacorrbinsensitive explosive on said base about said rods and tube. and removing said rods and base from said cast sheath to provide perforations through the sheath adapted to receive a detonating fuse.

References Cited by the Examiner UNITED STATES PATENTS BENJAMIN A. BCRCHELT, Primary Examiner.

ARTIIUR M. HORTON, SAMUEL BOYD, Examiners. 

1. THE METHOD OF MAKING A BOOSTER FOR INSENSITIVE EXPLOSIVES COMPRISING SUPPORTING A ROD ON A BASE IN UPSTANDING RELATION THERETO, WRAPPING A FLEXIBLE TUBE CONTAINING PRIMACORD-SENSITIVE EXPLOSIVE AROUND SAID ROD, COMPACTING A SHEATH OF PRIMACORD-INSENSITIVE EXPLOSIVE 